As shown in FIGS. 4 or 5, a conventional silent chain 1 is composed of a large number of plates 4' which are connected together in an endless fashion. The plates 4' are also connected together bendably through plural sets of rocker pins 2' and 3' with each set being constituted by two rocker pins. Teeth of a sprocket 5 come into engagement with engaging surfaces of the plates 4' to perform the transmission of power between the sprocket 5 and another sprocket (not shown). The plates 4' are arranged in many rows in the transverse direction of the silent chain 1 in such a manner that the plates, which are adjacent to each other back and forth in the traveling direction of the silent chain 1, are sandwiched alternately in the transverse direction.
Of the two rocker pins 2' and 3' which constitute each set, one rocker pin 2' is longer than the other rocker pin 3'. An end of each rocker pin 2', 3' is fitted in non-circular pin holes formed in plates 4'A. The plates 4'A are arranged adjacent both outsides of the plural, transversely arranged plates 4' and are guided by side faces of the teeth of the sprocket 5.
FIG. 6 a side view of each plate 4' and a pair of rocker pins 2' and 3' are inserted into each of the pin holes 6' and 7' through the plate 4'. The rocker pins 2' and 3' have the same cross-sectional shape and are inserted into each of the pin holes 6' and 7' so as to be opposed to each other so that the rocker surfaces 2'B and 3'B of the rocker pins 2', 3', respectively, are adjacent to each other.
The rocker pins 2' inserted into the pin holes 6' and 7', and located closer to the outer end of the plate 4', have respective concavely arcuate plate abutting surfaces 2'A formed on the side opposite to their rocker surface 2'B. The plate abutting surfaces 2'A come into engagement with convexly arcuate pin seating surfaces 6'A and 7'A and are thereby prevented from rotating. The inner peripheral portions, other than the pin seating surfaces 6'A and 7'A of the pin holes 6' and 7', are each formed by a simple concavely arcuate surface.
On the other hand, the rocker pins 3', inserted into the pin holes 6' and 7' and located closer to the center of the plate 4', are each engaged at a plate abutting surface 3'A thereof with pin seating surfaces 6'A and 7'A of a pin holes 6', 7' formed in a longitudinally adjacent plate (not shown).
As shown in FIG. 4, when the silent chain 1 is entrained on the sprocket 5 and a tensile force is exerted between front and rear plates, the rocker surface 2'B of the rocker pin 2' and the rocker surfaces 3'B of the rocker pin 3' are pressed against each other to effect transfer of the tensile force.
Since the opposed rocker surfaces 2'B and 3'B are each formed in a convexly arcuate shape, it becomes possible to perform a relative rocking motion between the rocker pins 2' and 3', thus permitting bending between longitudinally adjacent plates. As shown in FIG. 6, a lower edge 8' of the plate 4' is bifurcated for engagement with the sprocket teeth, while an upper edge 9' thereof is formed as a flat surface.
In the conventional silent chain constructed as described above, the convexly arcuate pin seating surfaces 6'A, 7'A of each of the pin holes 6', 7' of the plate 4' and the concavely arcuate plate abutting surfaces 2'A, 3'A of the associated rocker pins 2', 3', respectively, which is closer to the outside of the plate 4', are brought into engagement with each other to prevent the rotation of the rocker pin 2', 3' relative to the plate 4'. Therefore, the area of contact between the pin seating surface 6'A, 7'A and the plate abutting surface 2'A, 3'A is small, with the result that while the silent chain is in use, the rocker pin 2', 3' closer to the outside of the plate 4' is apt to wobble within the pin hole 6', 7' of the plate 4'. This has so far been a cause of power loss during travel of the silent chain.
Further, when a tensile force is exerted between adjacent plates during use of the silent chain, each pin hole is elastically deformed in an elliptical shape longitudinally and microscopically. In this case, at both circumferential ends of the pin seating surface which is formed in a convexly arcuate shape, the contour of the inner peripheral surface of the pin hole is suddenly transformed into a concavely arcuate shape. Consequently, stress is concentrated on both end portions. Stress concentration occurs also at the central, upper and lower portions of the inner peripheral surface of each pin hole and at the inwardly recessed portion of each plate, so that the plate is likely to be cracked and broken from those portions due to metal fatigue.
Accordingly, it is an object of the present invention to solve the above-mentioned problems of the prior art and provide a silent chain, as well as a rocker pin and plate thereof, capable of enhancing the transmission efficiency and improving the fatigue strength of the plate to prolong the service life of the chain.